A research group of University of Birmingham makes reference to 1-(2-fluoro-4-thio-beta-D-arabinofuranosyl)-5-methyluracil and 1-(2-fluoro-4-thio-beta-D-arabinofuranosyl)-5-iodocytosine in International Patent Application PCT/GB90/01518 (International Publication Number: WO 91/04982).
Further, a research group of NIH has recently made a report on such compounds as 1-(2,3-dideoxy-2-fluoro-4-thio-beta-D-erythro-pentafuranosyl)uracil represented by the following formula: ##STR2## provided that B is uracil in series a, and cytosine in series b (Tetrahedron Letters, 35, 7569-7572 (1994); Tetrahedron Letters, 35, 7573-7576 (1994); Chemistry Letters, 301-302 (1995)).
However, the group of University of Birmingham describes the above two compounds as mere instances, and fails to show examples in which they were practically synthesized. Moreover, although a process for producing the compounds is explained in the specification for the aforementioned international patent application, the process is simply an application of those processes which are described in known references (J. Org. Chem., 50, 2597 (1985), J. Org. Chem., 50, 3644 (1985)). It is clear from the above-described reports made by the group of NIH that desired compounds can never be obtained by employing such a process. The specification for the foregoing international application slightly makes mention of the antiviral activity of the compounds, but is quite silent on specific data in terms of the activity.
Further, although the group of NIH makes reference to the anti-HIV activity of the compounds synthesized, the activity is not necessarily satisfactory.
Furthermore, both of the groups have made no report on other biological activities than antiviral activity.